Hydraulic motors in a closed hydraulic circuit, and, in particular, in a respective one thereof, are used in many self-propelled road pavers for the travel drive and further drives. The hydraulic motors are pressurized with hydraulic oil by hydrostatic pumps (designated below as operating pumps for the purpose of better distinguishability), which in turn are driven by an internal combustion engine, for example. The term operating pump thus designates in the present case a hydraulic pump which conveys the hydraulic oil within a closed hydraulic circuit for driving a consumer. A specific quantity of the hydraulic oil is usually taken from the circuit per unit of time for the exchange of hydraulic oil (for example, for cooling or cleaning purposes) in the closed circuit, which quantity is replaced at another location by a cooled and filtered hydraulic oil, so that the total quantity of the hydraulic oil in the closed hydraulic circuit ideally remains approximately constant. This process is known in the present case as scavenging. The supply of the hydraulic oil to the closed hydraulic circuit during the scavenging process usually occurs by means of constant pumps with a constant volumetric displacement. The pump output is configured in such a way that during the operation of the circuit under loading of the hydraulic motors and simultaneously at a low hydraulic oil flow rate, i.e., at low speed of the internal combustion engine, an oil supply is ensured which is sufficient for the compensation of the hydraulic oil volume taken from the closed hydraulic circuit per unit of time. In order to ensure an oil supply which is adequate over the entire operating spectrum, the delivery rate of the constant pump is therefore always designed for oversupply of the circuit with hydraulic oil, wherein excess amounts are lost as power losses. This produces unnecessary consumption of fuel. Furthermore, problems frequently occur during starting, especially during cold starting of the internal combustion engine, because the produced drag loads are very high. A generic road paver is known, for example, from DE 10 2011 018 469 A1.
The present invention is based on the object of providing a method, a hydraulic system and a road paver of the kind mentioned above with which the fuel consumption of the internal combustion engine can be reduced and at the same time the required dragging power can be reduced, especially during cold starting.